I agree with DivaDevotee because I've heard that Jill is classically trained...she used to sing 'opera' and I think has busted out an aria at a performance or two. I mean, I'm not super knowledgeable about technical things but I think this is right.

Jill is a Soprano, she mostly uses her low and mixed mid high notes in most of her songs, listen to the high parts, she has the same timbre Soprano voice comparable to Kelly Clarkson and Patty Labelle's

I agree with this. Dramatic sopranos are often confused with contraltos to due their dark, heavy timbre. One must check the tessituras and comfortable ranges to make the distinction. Also, even though dramatic sopranos tend to be very dark for soprano standards, their actual vocal weight tends to still be lighter than the most traditional contraltos.

The underlying timbre could be apparent in other registers. If she has a developed chest register, that could give her sound more of a heavy, darker tone either way. But this darkness would probably be apparent in the head voice, too, if she were a dramatic soprano. Their head voices are not as light as lyric sopranos.